Mesonephros

One of a pair of excretory organs (mesonephroi) which grow caudally to the first pair (pronephroi) during development. Mesonephroi are the permanent kidneys in adult amphibians and fish. In higher vertebrates, proneprhoi and most of mesonephroi degenerate with the appearance of metanephroi. The remaining ducts become WOLFFIAN DUCTS.